KR20190030348A - Electrode catalyst for fuel cell, membrane-electrode assembly for fuel cell, fuel cell, and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a catalyst for a fuel cell electrode, a membrane-electrode assembly for a fuel cell, a fuel cell, and a method for manufacturing the same. More particularly, the present invention relates to a catalyst for a fuel cell electrode comprises: a carbon spheres cluster in which a plurality of carbon spheres are connected; and an active metal supported on the carbon spheres cluster, and to a membrane-electrode assembly for a fuel cell, a fuel cell, and a method for manufacturing the same. The present invention can provide a catalyst for a fuel cell capable of enhancing the utilization of the catalyst and capable of excellent water management and excellent gas diffusion during high current operation.

Description

TECHNICAL FIELD [0001] The present invention relates to a catalyst for a fuel cell electrode, a membrane-electrode assembly for a fuel cell, a fuel cell, and a method for manufacturing the same. BACKGROUND ART [0002]

The present invention relates to a catalyst for a fuel cell electrode, a membrane-electrode assembly for a fuel cell, a fuel cell, and a method for manufacturing the same.

Vulcan and ketjen black, which are used as carbon supports for general PEMFC catalysts, have a primary particle size of 30-50 nm and primary particles form agglomerates of several hundred nm size. Aggregates clump together and exist in larger aggregates. The Pt catalyst supported at not less than 40% by weight is distributed not only on the outer side of the primary particles but also on the inner fine pores. Through the contact with the ionomer used as the positive ion conductor in the electrode production, the active site of the fuel cell oxygen reduction reaction (ORR) A triple phase interface or boundary is created.

Conventional commercial catalysts are based on platinum present between platinum and agglomerates present in the internal micropore of carbon black particles, regardless of the form of long side chain ionomer or short sidechain ionomer There is a problem in that the ionomer can not permeate and the platinum utilization rate for the ORR reaction is lowered.

In order to prevent the platinum utilization rate from lowering, attempts have been made to remove fine pores existing in the carbon black such as volcanic, Ketjenblack or the like through heat treatment at an elevated temperature under an inert gas atmosphere. That is, the surface area is reduced and the platinum utilization is improved through the post-treatment graphitization process at a high temperature. However, in the case of the graphitized carbon black, The flooding phenomenon occurs due to excess water generated in the high current operation region and an inefficient water management phenomenon occurs in which oxygen supply for the ORR reaction becomes difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a catalyst for a fuel cell electrode which can increase the catalyst utilization rate and can perform excellent water management in high current operation.

The present invention provides a membrane-electrode assembly for a fuel cell comprising the catalyst for a fuel cell electrode according to the present invention.

The present invention provides a fuel cell including a membrane-electrode assembly for a fuel cell according to the present invention.

The present invention provides a method for producing a catalyst for a fuel cell electrode according to the present invention.

According to one aspect of the present invention,

A carbon spheres cluster in which a plurality of carbon spheres are connected; And an active metal supported on the carbon sphere cluster; To a catalyst for a fuel cell electrode.

According to one embodiment of the present invention, the carbon spheres may have a size of 100 nm or more.

According to an embodiment of the present invention, the carbon sphere cluster may include a non-porous carbon spheres, a porous carbon spheres, or both.

According to an embodiment of the present invention, the porous carbon sphere may include pores of less than 2.0 nm.

According to an embodiment of the present invention, the active metal may be supported in an amount of 5 to 30 parts by weight based on 100 parts by weight of the catalyst for a fuel cell electrode.

According to one embodiment of the present invention, the active metal may have a size of 2 nm or more.

According to one embodiment of the present invention, the active metal may be supported on the surface of the carbon spheres.

According to one embodiment of the present invention, the carbon sphere clusters may have a specific surface area of 10 to 30 m ² / g.

According to another aspect of the present invention,

Waterproof; Air pole; And a polymer electrolyte membrane between the hydrogen electrode and the air electrode; Wherein the air electrode comprises a catalyst layer comprising a catalyst for a fuel cell electrode according to the present invention.

According to one embodiment of the present invention, the thickness of the air electrode may be 0.1 탆 to 50 탆.

According to an embodiment of the present invention, the catalyst layer may form a single or multiple catalyst layers.

According to an embodiment of the present invention, the active metal in the membrane-electrode assembly for a fuel cell may be contained in an amount of 0.01 to 0.5 mg / cm ² .

According to an embodiment of the present invention, the average pore size of the catalyst layer may be 100 nm to 1500 nm.

According to an embodiment of the present invention, the active metal utilization in the catalyst layer may be 80% or more.

Another aspect of the present invention relates to a fuel cell including a membrane-electrode assembly according to the present invention.

According to yet another aspect of the present invention,

Preparing a polymer electrolyte membrane; And a catalyst layer comprising the catalyst for a fuel cell electrode according to the present invention; Electrode assembly for a fuel cell.

According to an embodiment of the present invention, the forming the catalyst layer may include: coating a slurry containing a catalyst for a fuel cell electrode on at least one surface of the polymer electrolyte membrane; . ≪ / RTI >

According to an embodiment of the present invention, the step of forming the catalyst layer includes: coating a slurry containing a catalyst for a fuel cell electrode on a substrate; And transferring the coating film formed in the coating step to at least one side of the polymer electrolyte membrane; . ≪ / RTI >

According to one embodiment of the present invention, the coating step may use a doctor blade coating method.

According to an embodiment of the present invention, the blade gap can be adjusted by coating the doctor blade coating.

According to one embodiment of the present invention, the coating step may be performed such that the longest portion in the x, y and z axial directions of the carbon sphere cluster is in contact with the substrate or the electrolyte membrane.

The present invention can provide a fuel cell catalyst capable of improving the utilization of the catalyst and capable of excellent water management and excellent gas diffusion during high current operation.

The present invention can provide a catalyst for a fuel cell having improved electron transfer and hydrogen ion transfer characteristics as compared with a conventional carbon structure catalyst.

INDUSTRIAL APPLICABILITY The present invention can prevent carbon corrosion during high-current operation to prevent degradation of the performance of a fuel cell.

1 shows a catalyst for a fuel cell according to an embodiment of the present invention.
FIG. 2 illustrates a cathode of a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention. FIG.
3 shows a process of a method for manufacturing a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention.
4 is an SEM image of a catalyst for a fuel cell manufactured in an embodiment of the present invention, according to an embodiment of the present invention.
5 is an SEM image of a membrane-electrode assembly for a fuel cell manufactured in an embodiment of the present invention, according to an embodiment of the present invention.
6 illustrates performance of a unit shell using the membrane-electrode assembly for a fuel cell according to an embodiment of the present invention and a comparative example according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. Also, terminologies used herein are terms used to properly represent preferred embodiments of the present invention, which may vary depending on the user, intent of the operator, or custom in the field to which the present invention belongs. Therefore, the definitions of these terms should be based on the contents throughout this specification. Like reference symbols in the drawings denote like elements.

The present invention relates to a catalyst for a fuel cell electrode. According to one embodiment of the present invention, the catalyst for a fuel cell electrode can improve utilization of active metals and improve water management and performance of the fuel cell .

According to an embodiment of the present invention, the catalyst for a fuel cell electrode may include a carbon spheres cluster in which a plurality of carbon spheres are connected; And an active metal supported on the carbon sphere cluster; . ≪ / RTI >

Referring to FIG. 1, FIG. 1 illustrates a catalyst for a fuel cell electrode according to an embodiment of the present invention. Referring to FIG. 1 (a), a carbon sphere cluster And (b) is a carbon spherical cluster carrying the active metal as the catalyst support. The carbon spherical clusters are formed by chemically bonding a plurality of carbon spherical particles. The carbon spherical clusters can reduce the electron transport resistance by reducing the interface between the carbon spheres in the catalyst layer. In other words, although the carbon sphere has many interfaces between the carbon nodules when the catalyst layer is formed independently, when the carbon nodular clusters are applied, the interface between the carbon nod clusters is small and pores can be formed therebetween. In addition, the carbon sphere cluster can lower the carbon corrosion phenomenon occurring at a high voltage in the operation of the fuel cell.

In one embodiment of the present invention, the carbon spheres have a diameter of 100 nm or more; Or 100 nm to 500 nm; Or a diameter of 100 nm to 300 nm. If the diameter is within the above-mentioned range, the interface between the carbon spherical clusters in the catalyst layer can be reduced, and large pores are formed between and / or around the carbon spherical clusters.

In one embodiment of the present invention, the carbon spherical clusters may include non-porous carbon spheres, porous carbon spheres, or both, and preferably non-porous carbon spheres. The porous carbon spheres may include pores similar to or smaller than the size of the active metal particles, and may include pores of less than 2.0 nm, for example. That is, the carbon spherical clusters can be formed by applying a non-porous carbon spherical and / or porous carbon spheres to improve the possibility of contact between the active metal and the ionomer by supporting the active metal on the surface or the surface of the carbon spherical cluster, Can be reduced.

In one embodiment of the present invention, the active metal may be supported in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the fuel cell electrode catalyst.

For example, the active metal may be selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Se, Rh, Pd, Ag, Cd, In, Sn, , Pt, Au, Hg, Pb, Ru, and Bi.

In one example of the present invention, the active metal has a thickness of 2 nm or more; 2 nm to 100 nm; 2 nm to 50 nm; Or a particle size of 2 nm to 10 nm.

In one embodiment of the present invention, the active metal may be supported on the surfaces of the carbon spheres, for example, non-porous carbon spheres, porous carbon spheres or both.

In one example of the present invention, the carbon spherical clusters may have a specific surface area of 10 to 30 m ² / g.

In one embodiment of the present invention, the carbon sphere cluster has a diameter of 1 占 퐉 or more; And may include a size of 1 mu m to 20 mu m or 1 mu m to 10 mu m. That is, the size may mean the longest portion in the x, y, and z axis directions of the carbon sphere cluster. When the size of the carbon sphere cluster is within the above range, macro pores of 500 nm or more are formed, and a large pore volume and a void fraction can be ensured. Therefore, The efficiency can be improved.

The present invention relates to a membrane-electrode assembly for a fuel cell according to the present invention, wherein the membrane-electrode assembly for a fuel cell includes a catalyst for a fuel cell electrode according to the present invention, It is possible to improve oxygen gas transfer and hydrogen ion transfer characteristics.

According to an embodiment of the present invention, the membrane-electrode assembly for a fuel cell includes: a hydrogen electrode; Air pole; And a polymer electrolyte membrane between the hydrogen electrode and the air electrode; . ≪ / RTI >

In one embodiment of the present invention, the air electrode may include a catalyst layer including a catalyst for a fuel cell electrode according to the present invention. H ⁺ protons (cations) are transferred to the carbon-sphere clusters of the catalyst layer through the cation conductors (ionomers) of the polymer electrolyte membrane of the polymer electrolyte membrane and the oxygen reduction reaction (ORR) at the three- reaction occurs.

  Referring to FIG. 2, FIG. 2 illustrates a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention. Referring to FIG. 2, the catalyst layer includes a carbon cluster- So that large pores are formed between and around the carbon sphere clusters due to the network between the carbon sphere clusters. Therefore, the flooding is alleviated due to the large pore, the diffusion of oxygen is smooth, the solid ionomer binder penetrates into the carbon sphere well, and the catalyst coating property of the ionomer binder acting as the hydrogen ion passage and the formation of the ionomer binder network become easy The hydrogen ion transfer characteristic can be improved. In addition, the network formation between the carbon sphere clusters can reduce the interface between carbon spheres and reduce the electron transfer resistance.

According to one embodiment of the present invention, the thickness of the air electrode is 0.1 mu m to 50 mu m; Or from 0.5 [mu] m to 20 [mu] m. The catalyst layer may form a single or multiple catalyst layers.

According to an embodiment of the present invention, the active metal in the membrane-electrode assembly for a fuel cell may be contained in an amount of 0.01 to 0.5 mg / cm ² .

According to one embodiment of the present invention, the average pore size of the catalyst layer is 100 nm or more; 100 nm to 1500 nm; Or from 500 nm to 1500 nm. When included within the pore size range, water management and oxygen gas delivery can be improved.

According to one embodiment of the present invention, the active metal utilization in the catalyst layer is 80% or more; 85% or more; Or 90% or more.

According to an embodiment of the present invention, the anode may be configured to be applicable in the technical field of the present invention, as long as the anode does not depart from the scope of the present invention.

According to one embodiment of the present invention, a fuel cell including the membrane-electrode assembly according to the present invention can be provided. The configuration of the fuel cell may include a configuration applied in the technical field of the present invention, without departing from the object of the present invention.

The present invention relates to a method for manufacturing a membrane-electrode assembly for a fuel cell according to the present invention, the method comprising: preparing a polymer electrolyte membrane; And a catalyst layer comprising a catalyst for a fuel cell electrode; . ≪ / RTI >

As an example of the present invention, the step of preparing a polymer electrolyte membrane is a step of preparing a polymer electrolyte membrane applicable to a fuel cell.

For example, the polymer electrolyte membrane includes a polymer electrolyte for diffusion of reaction products, ions, and the like. The polymer electrolyte can be used without limitation as long as it is applicable to fuel cells in the technical field of the present invention. For example, the polymer electrolyte can be a polyarylene ether sulfone (S-PES), a sulfonated polybenzimidazole S-PBI), sulfonated polyether ketone (S-PEEK), poly (para) phenylene (S-PP), sulfonated polyimide (S- PI), sulfonated polysulfone A sulfonated hydrocarbon-based polymer such as a sulfone-based polymer; (Nafion, DuPont), Flemion (Asahi Glass), Asiplex (Asahi Chemical), Dow XUS (Dow Chemical), Aquivion (Solvay) Overfed digestive system polymer; A benzimidazole-based polymer, and a polyimide-based polymer; Polyetherimide type polymers; Polyether ketone type polymers; Polyether-ether ketone-based polymers; And polyphenylquinoxaline-based polymers; And the like, but the present invention is not limited thereto.

For example, a polymer electrolyte can be impregnated in a porous support, and the porous support can be used without limitation as long as it is a porous support applicable to a fuel cell. Examples of the support include polytetrafluoroethylene (PTFE), polyethylene (PE But is not limited to, at least one member selected from the group consisting of polyvinylidene fluoride (PVDF), polyimide (PI), polypropylene (PP), cellulose and nylon.

According to an embodiment of the present invention, the step of forming the catalyst layer including the catalyst for the fuel cell electrode is a step of forming a catalyst layer including the catalyst for the fuel cell electrode according to the present invention on at least one surface of the polymer electrolyte membrane.

According to an embodiment of the present invention, the step of forming a catalyst layer including a catalyst for a fuel cell electrode includes the steps of: coating a slurry containing a catalyst for a fuel cell electrode on at least one surface of the polymer electrolyte membrane; . ≪ / RTI >

According to an embodiment of the present invention, the step of forming a catalyst layer including a catalyst for a fuel cell electrode includes the steps of: coating a slurry containing a catalyst for a fuel cell electrode on a substrate; And transferring the coating film formed in the coating step to at least one side of the polymer electrolyte membrane; . ≪ / RTI >

In one embodiment of the present invention, the step of coating the catalyst slurry is a step of coating a catalyst slurry on at least one surface of a substrate or a polymer electrolyte membrane by a doctor blade coating method.

For example, the substrate can be applied without restriction as long as the substrate is a separable substrate, and can be, for example, glass, a wafer, or the like.

For example, the thickness of the catalyst layer can be controlled through gap control of the blades during the doctor blade coating. This can be accomplished by lengthening the carbon core clusters having a long vertical direction. Therefore, the thickness of the catalyst layer can be controlled by aligning the catalyst layer with the desired height and controlling the size of the carbon spheres.

 Referring to FIG. 3, FIG. 3 illustrates a process for producing a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention. In FIG. 3, x, y, and z For example, La (horizontal), Lb (height), and Lc (depth) are set so that the longest portion in the axial direction is coated in contact with the electrolyte membrane, , The longest part of them is coated on the electrolyte membrane. In addition, the remaining two lengths are the height of the catalyst layer, and the thickness of the catalyst layer can be designed by controlling the basic size of the carbon sphere of the carbon sphere cluster.

The present invention is not limited thereto but may be embodied in other specific forms without departing from the spirit or scope of the present invention as set forth in the following claims, The present invention can be variously modified and changed.

Example

(1) Production of carbon spherical clusters

500 ml of 1M D-glucose (D-glucose, Aldrich chemical) aqueous solution is put into a 600 ml capacity autoclave coated with Teflon, and the inside of the reactor is purged several times with nitrogen to remove oxygen in the reactor. Using an agitator, the aqueous solution of D-glucose was uniformly stirred and heated to 180 ° C. It is possible to control the carbon clustering degree by controlling the stirring speed. After the hydrothermal synthesis reaction at 180 ° C for 3 to 5 hours, the reactor is cooled to room temperature. The cooled reactor is depressurized to normal pressure and black precipitates in the reactor are recovered. The recovered particles are recovered by using filter paper, and then washed several times until a clear filtrate is obtained by using ethanol, distilled water and acetone. The brown carbon spheres that have been filtered are dried overnight in a freeze dryer or vacuum oven, and then calcined in an N ₂ atmosphere at 1000 ° C. for 3 to 5 hours to produce carbon spherical clusters.

(2) Support of platinum

A carbon ball cluster was dispersed in 200 ml of ethylene glycol. 1.4 g of a solution of PtCl ₂ (5% by weight) was added to a solution containing 0.63 g of carbon spherical clusters, and the mixture was sufficiently stirred (based on 10% by weight in the total solution). The solution was titrated to pH 11 with 1.0 M sodium hydroxide (NaOH) solution and sufficiently stirred. Platinum (Pt) was synthesized by microwave deposition (the temperature was raised to 160 ° C within 1 minute and maintained at 160 ° C for 10 minutes). After cooling to room temperature, the carbon spherical clusters carrying platinum (Pt) were filtered and sufficiently washed with distilled water. Then, the prepared sample was rapidly frozen and then dried using a freeze dryer. The platinum supported on the carbon nanotubes was synthesized as particles of about 3 nm. The prepared fuel cell electrode catalyst can be found by TEM photographing that platinum (Pt) active metal particles are uniformly dispersed and attached to the surface of the carbon sphere cluster of the present invention.

(3) Preparation of membrane electrode assembly

(Dupont, NRE521) and 0.3 ml of an additional solvent (water / isopropyl alcohol 1: 1) per 0.1 g of a platinum-supported carbon spherical cluster (platinum The ink was prepared by stirring overnight in a paste mixer. The ink was coated on a transfer paper support using a doctor blade to form an electrode, followed by overnight drying at room temperature and normal pressure. The dried carbon spherical cluster electrode was decal-transferred onto a Nafion membrane (Dupont, NRE212) by hot pressing. (120 ° C, 150 bar) was used as a cathode, and the hydrogen electrode was manufactured using a commercially available Hispec 4000 (Johnson Matthey) as a membrane electrode assembly composed of a cathode layer / electrolyte membrane / oxygen electrode layer Respectively.

SEM images of the cross section of the platinum-carrying carbon spherical clusters and the membrane-electrode assembly are shown in FIGS. 4 and 5. FIG. 4 and 5, carbon spherical clusters having a plurality of carbon spheres connected to each other are formed, and carbon spherical clusters are coated on the electrolyte membrane, forming a network of carbon spherical clusters and forming pores therebetween .

Comparative Example

A membrane electrode assembly was prepared in the same manner as in Example 1, except that a cathode layer was formed using carbon balls.

Experimental Example

(1) Platinum utilization ratio and void space ratio of the catalyst layer

The platinum utilization ratio and the void space ratio of the catalyst layer according to each catalyst in the membrane electrode assembly were measured and shown in Tables 1 and 2.

Platinum utilization (%) = (ECSA of single cell / ECSA of RDE) * 100

ECSA: Electrochemical surface area

Table 1 shows that although the platinum cluster content according to the present invention has a low platinum content, platinum utilization rate is 80% or more.

As shown in Table 2, it can be seen that the void space ratio in the catalyst layer is higher than that of the commercial catalyst when the carbon ball cluster according to the present invention is applied.

(2) Evaluation of fuel cell performance

The membrane-electrode assemblies of Examples and Comparative Examples had a temperature of 70 DEG C; Humidity conditions RH 100%; Gas flow stoichiometry H _{2 /} air = 1.4 / 2.5; 1.2 A / cm ² standard; Usage H ₂ = 116 sccm; air = 500 sccm; Atmospheric pressure operation; The performance of a single cell composed of the membrane electrode assemblies of Examples and Comparative Examples was evaluated under the conditions of a Pt loading (cathode) of 0.06 mg _{pt /} cm ² and is shown in FIG.

Referring to FIG. 6, it can be seen that the performance of the fuel cell is improved when the carbon ball cluster according to the present invention is applied. This is because when the catalyst layer is formed as a carbon cluster, large pores are formed as compared with the independent carbon spheres, the electron transfer resistance can be reduced, and the oxygen gas transfer and the hydrogen ion transfer can proceed smoothly. In addition, due to the large carbon sphere size of 100 nm or more and the highly graphitized carbon spherical surface, it is possible to prevent carbon corrosion at high currents, thereby preventing deterioration of the performance of the fuel cell. Furthermore, the carbon spheres exist in the form of clusters attached to each other, so that the electron transfer resistance can be minimized.

Claims (21)

A carbon spheres cluster in which a plurality of carbon spheres are connected; And
An active metal supported on the carbon sphere cluster;
/ RTI >
Catalyst for fuel cell electrode.
The method according to claim 1,
Wherein the carbon spheres have a size of 100 nm or more.
The method according to claim 1,
Wherein the carbon sphere clusters include non-porous carbon spheres, porous carbon spheres, or both.
The method according to claim 1,
Wherein the porous carbon spheres contain pores of less than 2.0 nm.
The method according to claim 1,
Wherein the active metal is supported in an amount of 5 to 30 parts by weight per 100 parts by weight of the catalyst for a fuel cell electrode.
The method according to claim 1,
Wherein the active metal has a size of 2 nm or more.
The method according to claim 1,
Wherein the active metal is supported on the surface of the carbon spheres.
The method according to claim 1,
Wherein the carbon spherical clusters have a specific surface area of 10 to 30 m ² / g.
Waterproof;
Air pole; And
A polymer electrolyte membrane between the hydrogen electrode and the air electrode;
/ RTI >
Wherein the air electrode comprises a catalyst layer comprising the catalyst of claim 1. A membrane-electrode assembly for a fuel cell,
10. The method of claim 9,
Wherein the thickness of the air electrode is 0.1 占 퐉 to 50 占 퐉.
10. The method of claim 9,
Wherein the catalyst layer forms a single or multiple catalyst layers.
10. The method of claim 9,
Wherein the active metal in the membrane-electrode assembly for a fuel cell is contained in an amount of 0.01 to 0.5 mg / cm < ² >.
10. The method of claim 9,
Wherein the average pore size of the catalyst layer is 100 nm to 1500 nm.
10. The method of claim 9,
Wherein the active metal utilization ratio in the catalyst layer is 80% or more.
13. A fuel cell comprising the membrane-electrode assembly of claim 12.
Preparing a polymer electrolyte membrane; And
Forming a catalyst layer comprising the catalyst for a fuel cell electrode according to claim 1;
/ RTI >
A method of manufacturing a membrane-electrode assembly for a fuel cell.
17. The method of claim 16,
Wherein the forming of the catalyst layer comprises:
Coating a slurry containing the fuel cell electrode catalyst on the polymer electrolyte membrane; Wherein the membrane-electrode assembly includes a membrane-electrode assembly.
17. The method of claim 16,
Wherein the forming of the catalyst layer comprises:
Coating a slurry comprising a catalyst for a fuel cell electrode on a substrate; And
Transferring the coating film formed in the coating step onto the polymer electrolyte membrane; Wherein the membrane-electrode assembly includes a membrane-electrode assembly.
The method according to claim 17 or 18,
Wherein the coating step uses a doctor blade coating method.
20. The method of claim 19,
Wherein the blade gap is adjusted by coating the doctor blade coating, thereby forming a membrane-electrode junction body for a fuel cell.
The method according to claim 17 or 18,
Wherein the coating step is performed such that the longest portion in the x, y and z axial directions of the carbon sphere cluster is coated in contact with the substrate or the electrolyte membrane.

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